Shift current is a direct current generated from nonlinear light–matter interaction in a noncentrosymmetric crystal and is considered a promising candidate for next-generation photovoltaic devices. The mechanism for shift currents in real materials is, however, still not well understood, especially if electron–hole interactions are included. Here, we employ a first-principles interacting Green’s-function approach on the Keldysh contour with real-time propagation to study photocurrents generated by nonlinear optical processes under continuous wave illumination in real materials. We demonstrate a strong direct current shift current at subbandgap excitation frequencies in monolayer GeS due to strongly bound excitons, as well as a giant excitonic enhancement in the shift current coefficients at above bandgap photon frequencies. Our results suggest that atomically thin two-dimensional materials may be promising building blocks for next-generation shift current devices.

位移电流是由非中心对称晶体中的非线性光-物质相互作用产生的直流电流，被认为是下一代光伏器件的有希望的候选者。然而，在真实材料中移动电流的机制仍然不是很清楚，特别是如果包括电子 - 空穴相互作用。在这里，我们采用第一性原理在 Keldysh 轮廓上与实时传播相互作用的格林函数方法来研究在真实材料中连续波照明下非线性光学过程产生的光电流。由于强束缚激子，我们证明了在单层 GeS 子带隙激发频率下的强直流偏移电流，以及在带隙光子频率以上的偏移电流系数的巨大激子增强。